Glass substrates used in flat panel displays and solar cells have recently been increasing their sizes, thereby requiring cylindrical targets having a length of 3 m or more in order to form thin films on the substrates having thus increased sizes. Such long cylindrical sputtering targets are used in magnetron rotary cathode sputtering apparatus. A typical cylindrical sputtering target is formed by fixing a cylindrical target material onto a long cylindrical base, while a seamless pipe made of a metal is used as the cylindrical base in general. Polishing the whole surface of a long cylindrical base is uneconomical because of its cost and problematic in terms of processing accuracy. Therefore, only both end parts of the cylindrical base are polished so as to attach to the sputtering apparatus, while the part where the cylindrical target material is fixed is left as it is as the seamless pipe and thus incurs swells and warpages instead of becoming a true circle.
There is a case where a long cylindrical sputtering target is constructed by stacking 10 or more small-sized cylindrical target materials, while misalignments in stacking may cause steps between the outer peripheral faces of the cylindrical target materials. Further, a multi-divided cylindrical sputtering target constituted by a plurality of cylindrical target materials requires a divided portion where adjacent cylindrical target materials are arranged with a gap therebetween in order to prevent the cylindrical target materials from colliding with each other and breaking as being thermally expanded by plasmas during sputtering. In particular, steps are likely to occur between the outer peripheral faces of the adjacent cylindrical target materials in such a divided portion.
Known as a method for preventing steps from occurring in a flat type target in which a plurality of target members are arranged on a single backing plate is one (e.g., Patent Literature 1) in which a target member having a higher sputtering surface forms a slope on the sputtering surface on the divided portion side leading to a lower sputtering surface. However, this method makes it necessary to polish a target material, which is problematic in that a greater loss occurs in the target material.
Also known as a method for aligning the centers of a cylindrical target material and a cylindrical base is one (see, for example, Patent Literatures 2 and 3) aligning the centers by using a spacer slightly thinner than the gap between the cylindrical base and the cylindrical target material with reference to the outer peripheral face of the cylindrical base and the inner peripheral face of the target material. When a long cylindrical base is used in this method, however, there are cases where the cylindrical target material cannot be inserted into the cylindrical base, or the position of the cylindrical target material is restricted by the form of the cylindrical base so that steps occur between the outer peripheral faces of adjacent cylindrical target materials.